Fishery biology of the goldfish

The fishery biology of the goldfish Carassius auratus was studied in Lake Trasimeno by analysing the selectivity of the equipment that can be used to control this invasive species. Sampling was conducted monthly from February 2003 to January 2004 by means of electrofishing, fyke-nets and gill-nets of different-sized mesh (22, 25, 28, 35, 40, 50, 70 and 80 mm). The average value of the CPUEs of goldfish caught was 10175.48 g·10−2·m−2 for gill-nets, 246.97 g·h−1 for fyke-nets and 606.50 g·min−1 for electrofishing. The efficiency of electrofishing was not uniform in all periods of the year, the mean CPUEs being highest in spring, when specimens of reproductive age were preferentially caught. Gill-nets yielded abundant catches of goldfish in all seasons, and displayed good sampling efficiency even in winter. With regard to the selectivity of gill-nets, estimated optimum selection lengths for each mesh size were: 11.92 cm, 13.55 cm, 15.18 cm, 18.97 cm, 21.68 cm, 27.10 cm, 37.94 cm and 43.36 cm. The results of this research demonstrate that the various fishing techniques can be effectively combined with the aim of controlling the goldfish population in Lake Trasimeno.